The present invention relates to a piezoelectric actuator in which a marking is formed at an electrode pattern on a piezoelectric element and a method of compensating a direction thereof.
In recent times, in the field of a micromotor, a piezoelectric actuator utilizing a piezoelectric element subjected to predetermined polarization processing has attracted attention.
In the procedure of fabricating the piezoelectric actuator, there is utilized a marking produced by forming a shape of an electrode pattern in identifying directions of polarization of respective divided electrodes in polarization processing, identifying a direction of a set position of the piezoelectric element in forming an electrode pattern for shortcircuiting, in identifying a direction of pasting a piezoelectric element on an elastic member in pasting operation, in identifying a direction of assembling a motor in assembling operation and in identifying a direction of attaching lead wires in attaching operation.
FIG. 17 shows a plane structure of a piezoelectric actuator according to a conventional example.
A piezoelectric actuator 100 according to the conventional example is installed with a piezoelectric element 101 produced by dividing a circular disk body in a fan-like shape in the peripheral direction, an electrode pattern 102 formed with electrodes 102a, 102b, 102c, 102d, 102e and 102f at every other divided portion in the fan-like shape of the piezoelectric element 101 in which the electrodes are shortcircuited at outer peripheral portions thereof, an electrode pattern 103 formed with electrodes 103a, 103b, 103c, 103d, 103e and 103f similarly in a fan-like shape in which the electrodes are shortcircuited at inner peripheral portions thereof and an entire face electrode, not illustrated, formed on a side of the piezoelectric element 101 opposed to the electrode patterns 102 and 103, and further formed with a marking 104 in a semicircular shape at a portion of the outer peripheral portion of the electrode 102a in the fan-like shape of the electrode pattern 102 (for example, refer to JP-A-1-283074, JP-A-3-219681).
However, the above-described marking 104 in the semicircular shape cannot be set with an area larger than that illustrated above to avoid overlapping the entire face electrode formed on the opposed side.
Further, when the divided electrode 102a in the fan-like shape and the piezoelectric element 101 are formed to shift from each other, there also causes a situation in which the position of the marking 104 cannot be detected by an image processing apparatus. The reason is as follows.
1) When a portion of the marking 104 rests on the outer periphery of the piezoelectric element 101, the area of the marking 104 is extremely reduced in accordance with the radius of curvature of the circle.
2) The marking 104 is deviated from the outer periphery of the piezoelectric element 101 and the marking is not formed at all.
3) An area of a blank margin portion in a ring-like shape between the divided electrode 102a in the fan-like shape and the outer periphery of the piezoelectric element 101 (portion not formed with the electrode pattern 102) is widened and the marking 104 cannot be discriminated from the blank margin portion.
Further, when dirt or dust having a shape and a size similar to those of the marking 104 is adhered to the electrode pattern 102 or 103, there poses a problem in which the correct position of the marking cannot be detected.
It is an object of the invention to provide a piezoelectric actuator and a method of compensating a direction thereof promoting a function of identifying a marking and minimizing adverse influence on a marking even when an electrode pattern is formed to shift.
That is, according to solving means of the problem, there is provided a piezoelectric actuator characterized in that in a piezoelectric actuator having a piezoelectric element forming an electrode pattern:
wherein the electrode pattern is formed with at least one marking in a shape comprising multiple sides (When the shape is closed, a polygonal shape is constituted. The same as follows.) for determining a direction of forming the electrode pattern of the piezoelectric element.
In the above-described solving means, the shape of the marking includes a shape comprising three sides (When the shape is closed, a tetragonal shape is constituted. The same as follows.), a shape comprising four sides (When the shape is closed, a pentagonal shape is constituted. The same as follows.) or other shape comprising multiple sides. Further, the position of the marking includes that of either of cases of forming the marking at an outer peripheral portion of the electrode pattern and at inside thereof.
The piezoelectric element includes shapes of a circular disk, a ring-like shape, a polygon and the like.
According to the solving means, the area surrounded by the shape comprising multiple sides becomes larger than an area surrounded by a semicircle and accordingly, the identifying function of the marking is promoted. Further, when the marking having the shape comprising multiple sides rests on the outer periphery of the piezoelectric element, the area is reduced in accordance with an internal angle of the shape comprising multiple sides and accordingly, a rate of reducing the area is smaller than that of reducing the marking in the semicircular shape.
Further, according to the piezoelectric actuator, the marking is featured in having a shape comprising three sides.
According to the solving means, an area surrounded by the shape comprising three sides becomes larger than the area surrounded by a semicircle and accordingly, the identifying function of the marking is promoted. Further, when the marking having the shape comprising three sides rests on the outer periphery of the piezoelectric element, the area is reduced by a constant rate and accordingly, the rate of reducing the area is smaller than that of reducing the marking in the semicircular shape.
Further, there is provided a piezoelectric actuator characterized in that in a piezoelectric actuator in which a piezoelectric element is divided in a peripheral direction and electrodes are formed at divided portions at least contiguous to each other to thereby constitute an electrode pattern:
wherein at least one marking for determining a direction of forming the electrode pattern of the piezoelectric element is formed on an inner side of an outer periphery of the electrode pattern and between the electrodes contiguous to each other in the electrode pattern.
In the above-described solving means, the shape of the piezoelectric element includes any of a circular disk shape, a ring-like shape, a polygonal shape and so on. Further, the respective electrodes formed at the divided portions include either of a system for connecting leads to the respectives and a system of shortcircuiting predetermined ones of the electrodes.
The shape of the marking includes a circular shape, a semicircular shape, a shape comprising two sides, a shape comprising three sides and other shapes comprising multiple sides as well.
According to the solving means, the marking is disposed on an inner side of an outer periphery of the electrode pattern and accordingly, even when the electrode pattern rests on the outer periphery of the piezoelectric element, no adverse influence is effected and sufficient identifying performance is ensured.
Further, there is provided a piezoelectric actuator characterized in that in a piezoelectric actuator having a piezoelectric element which is divided equally by n in a peripheral direction and in which p of consecutive divided portions polarized in one direction and p of consecutive divided portions polarized in a direction reverse to the one direction are alternately arranged and electrodes are formed at n of the divided portions of the piezoelectric element:
wherein the electrode pattern is formed with m of markings for determining a direction of forming the electrode pattern of the piezoelectric element at equal intervals (where m=n/(2xc3x97p), m: an optimum number of markings, n: a number of dividing the piezoelectric element, p: a number of consecution in the same polarization direction).
In the above-described solving means, the piezoelectric element includes any of a circular disk shape, a ring-like shape, a polygonal shape and so on.
The shape of the marking includes a circular shape, a semicircular shape, a shape comprising two sides, a shape comprising three sides and a shape comprising multiple sides as well. The position of the marking includes any of a case where it is formed at an outer peripheral portion of the electrode, a case where it is formed at inside of the electrode and a case where it is formed between electrodes.
According to the solving means, by recognizing any of the markings, a direction of polarization of the respective divided portion of the piezoelectric element can be specified. That is, the markings are formed at each unit (2xc3x97p) of an arrangement of a polarization direction polarized regularly and accordingly, when any of m of the markings is recognized, the directions of polarization of n of the divided portions become apparent. Further, the direction of the electrode pattern of the piezoelectric is compensated among the unit divided portions in the direction of polarization and accordingly, a rotational angle to be compensated for can be reduced.
Further, there is provided a method of compensating a direction of the piezoelectric actuator according to any one of the above-described piezoelectric elements, characterized in comprising the steps of:
recognizing the markings formed at the electrode pattern on the piezoelectric element, determining the direction of forming the electrode pattern of the piezoelectric element based on the recognized markings, determining an angle to be compensated by comparing the direction of forming and a set direction of the electrode pattern of the piezoelectric element and compensating the piezoelectric element in the set direction by pivoting the piezoelectric element by the compensated angle.
In the above-described solving means, the method of recognizing the marking includes either of a method by optical observation and a method by mechanical means of a camera or the like.
Further, the direction compensating method is used, for example, in adjusting a direction of the piezoelectric element when polarization is carried out, a direction of a set position of the piezoelectric element in forming the electrode pattern for shortcircuiting, a direction of pasting the piezoelectric element on an elastic body, a direction of assembling a motor in assembling operation and a direction of attaching lead wires in attaching operation.
According to the solving means, the marking formed at the electrode pattern on the piezoelectric element is clearly recognized, the direction of forming the electrode pattern of the piezoelectric element is determined based on the recognized marking, the angle to be compensated for is determined by comparing the direction of forming the electrode pattern of the piezoelectric element with the set direction and the piezoelectric element is compensated to the set direction by pivoting it by an amount of the angle of compensation.